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The incident appeared to be linked to an earlier attack on police officers Friday, in which a man shot at four national police officers from a car in the nearby city of Carcassonne. The driver tried to ram the officers over as they were out jogging. Police later found the same vehicle at the Super U in Trebes.

Images from the scene showed police vehicles and security officers surrounding the supermarket. An employee who fled the supermarket as shots were fired told BFM that he and around 50 others were in lockdown in the car park.

A BFM reporter at the scene said the attacker claimed to be an ISIS soldier and demanded the release of Salah Abdeslam, the suspected mastermind of the Paris attacks. The attacks, in November 2015, were the deadliest on French soil in the country’s modern history.

CNN could not independently confirm the demand. Abdeslam’s trial opened in Belgium in February this year.

French President Emmanuel Macron, who is in Brussels at an EU leaders’ summit, described the hostage incident as a “terror attack” and said he would return to the country promptly.

“Everything leads us to believe that it is indeed a terror attack which is, as I said, still ongoing. The police … intervened in a very coordinated manner after what was first an attack against police officers,” Macron said at a press conference alongside German Chancellor Angela Merkel.

“I myself will be back (in France) in a couple of hours in order to coordinate all the new measures that need to be taken.”

“We would like to express our sincere condolences. We stand firmly at Frances side at this terrible time when they have fallen victim to a terror attack.”

The Paris prosecutor’s office said it was opening an investigation into a terrorist act, as well as murder and attempted murder.

French Interior Minister Gérard Collomb arrived in Trebes Friday afternoon and earlier reported that a security cordon had been established in the area, he wrote on Twitter.

“Avoid the area and stay tuned to the instructions from authorities,” Collomb added

France had faced a string of terror attacks in recent years, including the Paris attacks and several smaller-scale assaults. France remained under a state of emergency status for around two years after the Paris attacks. It was lifted late last year.